Fault detection systems and methods for power grid systems

ABSTRACT

This application discloses a system that may comprise at least a portion of a supply network. The system may further comprise a load controller that controls current flow with a current level of I1 into a load network that provides power to one or more loads from the at least a portion of the supply network according to a preprogrammed load curve. The system may also comprise a protection system that isolates the at least a portion of the supply network from the load controller in response to detecting a current pattern that is inconsistent with the preprogrammed load curve.

This application claims priority to U.S. provisional application Nos.62/613,991, filed on Jan. 5, 2018, and 62/620,981, filed on Jan. 23,2018, the entirety which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to power grid systems. In particular, agrid system designed to use slow rates of change in the current providedto systems connected to the grid and using those slow rates of change toenable rapid fault detection.

Electrical power is traditionally distributed to customers as AC becauseit is a simple and cost-effective method in centralized power productionschemes. Conventional alternating current (AC) power grid systems usetechnology that is nearly 100 years old. The cost of implementingconventional AC power grid systems is based on commodities, such ascopper, steel, aluminum, wood, and oil, that continue to increase inprice.

Rapid improvements in cost and performance of photovoltaic (PV)technology, battery technology, and power electronics facilitate thedevelopment of DC power grid systems that can provide better efficiency,reliability, and safety at lower costs than AC power grid systems. Thecost improvements can be obtained from the economic savings of usinglower cost commodities, and from more active use of deployed equipment.

However, DC power grid systems have been slow to progress due tochallenges concerning control and protection of DC power grids. DC powergrid systems can respond to load/supply variations and fault conditionsquickly relative to AC systems. This characteristic combined withtime-varying supply and load configurations may result in DC power gridsystems that are specially designed and include complicated controlalgorithms to maintain stability. Additionally, fault conditions on DCdistribution networks may be a safety concern. For example, unlike ACdistribution networks, the constant direct flow of current to a DCsystem fault can be difficult to interrupt using cost effective means.

By designing a system that works with slow rates of change, inductancemay be added to the system to lower the di/dt of current, which makesthe system safer and able to operate with hardware with lower currentratings (e.g., fuses). The slow rates of change may also enhance thestability of the system and enable the use of voltage signalingtechniques that otherwise would be difficult on a system with randomvariations in system voltage.

Reliability of power distribution is a priority for the grid operators.The ability to quickly detect, isolate, and recover from faults in thedistribution system is critical for the reliability of the system. Theproliferation of distributed resources brings additional constrains tothe system operation that have to be addressed to maintain and increasethe reliability of the distribution system. Distribution systems usefuses and protection relays to isolate the different sections of thesystem in case of faults. When a fuse is blown because of overcurrent,service personnel have to be dispatched to the site to replace the fuseand restore the power service to those affected by the outage.

More advanced electronic protections based on measuring the current anddisconnecting in case of a fault can be installed and coordinated torespond earlier than the fuse and allow easy restoration of power aftera fault. These electronic protections may include fault distanceestimation, wavelet transforms, and differential current. Because of thehigh cost, advance methods are mainly used in larger feeders with fusesbeing the preferred method to protect smaller laterals and servicedrops. Protections are located to minimize the number of customersaffected by a fault. In addition, in some cases redundant paths of powerdistribution are provided for fast restoration of power while minimizingthe number of customers affected by outages.

Traditional fault detection schemes include a balancing strategy thatallows the system to react quickly to an imperfect match between thesupply and load behavior by a voltage variation, which indicates avoltage imbalance, and thus a current imbalance. Traditional systemsmust tolerate a wide range of operating currents such that even in faultconditions it takes time for the system to determine that the current isabnormal and constitutes a fault. These traditional systems rely on alarge energy flow to the fault to initiate protective action, creating ahigh chance for damage and safety concerns. In other words, theconventional overcurrent protections are activated by currents wellabove the nominal value of the line current, independently of thecurrent being demanded by the load at any instant. This is because thesystem cannot anticipate sudden load changes and differentiate them fromfault currents.

To accomplish these goals, the system can add communication between thesupply and load networks, either through wired or wireless communicationplatforms. The wired communication platforms typically requireindependent hardware installed solely for the communication. Theseplatforms require extra equipment, increasing the cost of the system.Wireless communication platforms also require additional hardwareinstalled into the system and can be unreliable. Both systems requiresignificant redesign every time a new network is created or added,further increasing the costs of providing or updating power networks.

As the power infrastructure changes by having more distributedgeneration and storage, new technologies are needed to take advantage ofthose resources and increase the reliability of the electricdistribution system. This is even more important in DC distributionsystems where different behavior results in the need for novelprotection methods. For example, the current rise after a fault in a DCsystem is generally much faster than for AC systems requiring fasterresponse from the protection methods as well as complicating thecoordination of the protections. In addition, restoration of power in DCdistribution systems is more difficult because of the large systemcapacitances that result in large inrush currents during re-energizationand potentially in resonances and damage to equipment.

To supply power from a DC distribution system to an AC system, aninverter may be used. An inverter is a device that transforms an DCsupply into an AC supply. Inverters accomplish this by using a switchingoperation, making the power flow in a wave rather than a direct path.The switching operation can range from a physical switch to a complexelectrical circuit utilizing semiconductors to operate a switch.

Inverters also vary in the shape of AC supply wave they create. These ACsupplies can be square waves, sinusoidal waves, or any other form ofwave dictated by the controlling software of the inverter. Differentapplications can tolerate different types of power signals. For example,complex electronics are very sensitive to the shape of the power wave,requiring smooth, sinusoidal waves to prevent damaging the internalcomponents. Large electronics, such as refrigerators and ovens, cantolerate more square waves without damaging their components.

Power grids must worry about faults. Faults can be dangerous for anumber of reasons, including danger to persons in the area of the faultby causing electrocution that could lead to ventricular fibrillation.Several types of faults exist, including ground faults, high impedancefaults, phase faults, pole to pole faults, arcing faults, intermittentpecking faults, voltage unbalance due to open neutral connections.

GFI faults are traditionally detected at the transformer with anexternal GFI device. This device passes two current carrying conductorsof an AC supply through a common current transformer. Both currentsinduce a magnetic field in the current transformer core. When thecurrents are in a balanced flow condition (or no fault condition), theopposing currents induce magnetic fields that cancel each other out,resulting in zero output voltage on the current transformer secondarywinding. When a ground fault occurs, a small amount of current isdiverted into ground and appears as an imbalance in the currenttransformer, thus generating a secondary voltage which quickly operatesthe GFI circuit breaker.

SUMMARY

This application discloses a system that may comprise at least a portionof a supply network. The system may further comprise a load controllerthat controls current flow with a current level of I₁ into a loadnetwork that provides power to one or more loads from the at least aportion of the supply network according to a preprogrammed load curve.The system may also comprise a protection system that isolates the atleast a portion of the supply network from the load controller inresponse to detecting a current pattern that is inconsistent with thepreprogrammed load curve.

This application also discloses a system where the supply network is anDC network. This application also discloses a system where the supplynetwork is an AC network. The system also discloses that the supplynetwork may comprise a supply controller that maintains a supply voltageof the supply network.

The application also discloses a system where the supply network furthercomprises an energy storage, wherein the supply controller maintains thesupply voltage using the energy storage. The system may also comprisethe supply controller is configured to vary the supply voltage to send acommunication pulse at a predetermined voltage or shape. The applicationalso discloses a system where the load controller comprises a voltagesensor, a processor, and a memory, wherein the memory includesinstructions that, when executed by the processor, cause the processorto extract the communication pulse from a power signal provided by thesupply network using the voltage sensor. The application also disclosesa system where the memory further comprises instructions that, whenexecuted by the processor, process the communication pulse to determinea command issued to the load controller.

The system may also comprise the processor determines the command basedon a length of time the supply voltage stays at the predeterminedvoltage. The system may also comprise the processor determines thecommand based on the shape of the power signal to or from the supplyvoltage. The system may also comprise the processor determines thecommand based on the rate at which the power signal transitions to thepredetermined voltage.

The system may also comprise varying the supply voltage to send thecommunication pulse comprises changing the supply voltage from aninitial level to the predetermined voltage at a rate slower than thenormal transience of a distribution line in the supply network.

The system may also comprise the processor determines a start of thecommunication pulse based on detecting the change in the supply voltageto the predetermined voltage at the set rate.

The system may also comprise sending the communication pulse furthercomprises ending the communication pulse by changing the supply voltagefrom the predetermined voltage at a set rate. The system may alsocomprise the processor determines an end of the communication pulsebased on detecting the change in the supply voltage from thepredetermined voltage at a set rate.

The system may also comprise the supply controller is further configuredto perform communication error correction by retransmitting thecommunication pulse if an expected response to a command communicated bythe communication pulse is not detected within a time period.

The application also discloses a system where the load controllercomprises a voltage sensor, a processor, and a memory, wherein thememory includes instructions that, when executed by the processor, causethe processor to detect a fault when the voltage sensor measures asupply voltage from the supply network that does not follow an expectedpattern set by the source controller.

The system may also comprise an energy storage in the load network, andthe load controller controlling the current flow comprises storing ordrawing energy from the energy storage to keep the controlled currentflow in accord with the preprogrammed load curve.

The application also discloses a system where the energy storagecomprises a storage controller and an energy storage device, the storagecontroller controlling storage or draw of energy from the energy storagedevice. The system may also comprise the storage controller communicateswith the load controller to adjust a position on the preprogrammed loadcurve based on the amount of energy stored in the energy storage device.The system may also be configured to where the energy storage devicecomprises a battery.

The system may also comprise the load controller changes levels on thepreprogramed load curve in response to demand of the one or more loads.

The application also discloses a system where the one or more loadscomprises a building. The application also discloses a system where theone or more loads comprises an inverter.

The system may also comprise the inverter comprises a memory; aprocessor; and a circuit for converting DC power to AC power. The thememory storage device may include instructions that, when executed bythe processor, perform a method comprising receiving an output of theinverter, storing the output of the inverter for multiple points intime, analyzing the output of the inverter for multiple points in timeto detect one or more faults, determining whether one or more of thedetected faults requires the inverter to enter one or more protectionmodes, and issuing a command to cause the inverter to enter one of theone or more protection modes based on the determination.

The system may also comprise the protection system comprises a componentthat limits the rate of change of a fault current.

The application also discloses a system where the component is aninductor.

The application also discloses a system where the protection systemcomprises a protection device, the protection device comprising acurrent sensing unit that measures a current; a controller that comparescurrent measurements from the current sensing unit to a predeterminedpattern; and a fast disconnect that receives a signal from thecontroller to act when a pattern of the measured current is inconsistentwith the predetermined pattern.

The system may also comprise comparing the current measurements from thecurrent sensing unit to the predetermined pattern comprises comparing aramp rate of the current measurements to a predetermined ramp rate. Thesystem may also be configured to where comparing the ramp rate of thecurrent measurements to the predetermined ramp rate comprisescalculating the derivative of the current measurements.

The application also discloses a system where the fast disconnectcomprises a solid-state device.

The system may also comprise detecting the current pattern that isinconsistent with the preprogrammed load curve is based on an observedramp rate. The system may also comprise detecting the current patternthat is inconsistent with the preprogrammed load curve is based on ashape of the current pattern. The system may also be configured to wheredetecting the current pattern that is inconsistent with thepreprogrammed load curve is based on a level of the current pattern.

The application also discloses a system where the load controller is afirst load controller, the current level of I₁ into the load network isa first current level of I₁ into a first load network, and thepreprogrammed load curve is a first preprogrammed load curve. The systemmay further comprise a second load controller that controls current flowwith a second current level of I₂ into a second load network from the atleast a portion of the supply network according to a secondpreprogrammed load curve. The application also discloses a system wherethe first preprogrammed load curve and the second preprogrammed loadcurve are the same. The application also discloses a system where thefirst preprogrammed load curve and the second preprogrammed load curveare different. The system may also comprise detecting the currentpattern that is inconsistent with the preprogrammed load curve comprisesdetecting the current pattern is inconsistent with both the firstpreprogrammed load curve and the second preprogrammed load curve.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example of a power grid system.

FIGS. 2-4 are preprogrammed load curves for various supply and loadcontrollers of the DC power grid system of FIG. 1.

FIG. 5 is an example of a pulse communication control scheme.

FIG. 6 is an example of a communication pulse.

FIG. 7 is a block diagram showing an example of a protection device.

FIG. 8 is a diagram showing an example of a smart inverter faultdetection system.

FIG. 9 is a flow chart illustrating the function of the software.

FIG. 10 is a diagram showing an example of smart inverter faultdetection system with the control unit integrated into the inverterdevice.

FIG. 11 is a block diagram showing an example of a power grid system.

FIG. 12 is a block diagram showing an example of a power grid system.

FIG. 13 is a block diagram showing an example of a power grid system.

FIGS. 14-16 are preprogrammed load curves for various supply and loadcontrollers of the DC power grid system of FIG. 1.

FIG. 17 is an example of a communication pulse.

DETAILED DESCRIPTION

The present disclosure describes systems and techniques related to apower grid system that can detect and clear faults earlier than otheralternatives while maintaining stable operation. In general, the powergrid system can utilize local energy storage to limit spikes in demandfrom loads. This enables stable control over the load curves in thegrid, which may then be used for fault detection based on variationsfrom the expected load curve. This stabilized control may preventnuisance trips that could otherwise be caused by spikes in load, such asthe cycling of an air conditioner compressor. The technique has anincreased value in DC grids where the dynamics of the system results inadded complications for fault detection and interruption. Nevertheless,AC grids may also benefit by providing early detection of faults,preventing blowing of fuses or tripping of circuit breakers, increasingreliability by enabling quick restoration of the power after a fault, aswell as other benefits.

For a DC grid, the described systems and techniques can be implementedso as to realize one or more of the following advantages. Embodiments ofa DC power grid system described in this specification are lower in costand more reliable than AC power grid systems. Relative to AC power gridsystems, embodiments of a DC power grid system described in thisspecification provide an easier interface or connection to renewable DCenergy sources such as a PV system. Embodiments of a DC power gridsystem described in this specification provide for DC configurations atload points, which enables the conversion of appliances and other loadsto DC. Effectively modular configurations of a DC power grid system canallow for easier underground installation and lower skilled labor, andrequire less or no customization for each application. Embodiments of aDC power grid system described in this specification provide inherentlysafer operation of the DC power grid that can be achieved due toswitching speed and programmable load behavior of power electronics incombination with distributed energy storage. Embodiments of a DC powergrid system and associated modular fail-safe designs can eliminate thecomplexity of many components of the AC power grid system and variationsin power line frequency, which may allow international consistency.

To facilitate effective communication, the invention also includes apulse signal communication platform that allows the network tocommunicate by sending a pulse signal where the voltage of the suppliedpower is set to a communicating voltage using a slow ramp up and rampdown of the voltage to a specified communicating voltage to indicate thepulse is a communication signal.

Hardware Overview

FIG. 1 is a block diagram showing an example of a power grid system 100that can detect and clear faults while maintaining stable operation andsupplying power to load networks. For example, when the power grid is aDC power grid, system 100 may be implemented as a stand-alonedistribution network with electrical energy being supplied by renewableand/or backup power generation sources and energy storage devices. TheDC power grid system 100 may be configured as a last mile applicationreplacing existing AC power grid systems and providing betterreliability while reducing peak AC system loading and avoidinggeneration or line capacity additions. The DC power grid system 100 maydeliver electrical energy over long distances and with higher levels ofpublic exposure relative to typical DC applications which are usuallyenclosed or contained within a building. By exploiting the use of energystorage devices and the programmability of power controllers, the DCpower grid system 100, with the storage and the controlled flows, mayprovide a distribution system that operates safely in and around publicareas. Intelligent use of energy storage devices, e.g., battery storageand the programmability of power controllers may overcome limitations ofconventional DC distribution systems relating to system stability andfault detection, fault clearing, and system control.

Supply Network

The DC power grid system 100 includes a supply network 102 and one ormore load networks, for example load networks 120 and 160. The supplynetwork 102 is connected with the load networks 120 and 160 by a DCdistribution circuit (not shown) having various possible voltages andconfigurations. Within the supply network 102 and load networks 120 and160 are converters that may have various configurations and may operatewith various supply and load shaping algorithms and preprogrammedcurves, which will be described in more detail below. In the illustratedembodiment of FIG. 1, the supply network 102 is shown deliveringelectrical energy with a current level of I₁+I₂+ . . . +I_(n) to theload network. Although one supply network 102 and two load networks 120and 160 are shown for purposes of explanation, the DC power grid system100 may include more than one supply network and/or one or more loadnetworks. In some embodiments, a load network may transform and act as asupply network, which is enabled through bidirectional converters, localenergy sources, and/or local energy storage. In some embodiments, theload network may be provided with a protection system equivalent to theprotection device 110 in the source network 102 giving it the fullfunctionality of a source network.

The supply network 102 may include a power source 108 that generatespower. The power source 108 may include, for example, a PV system thatemploys a solar panel array to generate DC electrical power, ahydroelectric power system that employs water turbines to generate DCelectrical power, a wind farm that employs wind turbines to generate DCelectrical power, a distributed natural fossil fuel generation system, abattery source, and/or an AC grid through a rectifier. The power source108 may include a main power source (e.g., the PV system) and a backuppower source (e.g., the hydroelectric power system, the wind farm, thedistributed natural fossil fuel generation system, other DC gridsystems, and/or the AC grid through the rectifier). In someimplementations, the power source 108 also includes one or morebatteries of appropriate size(s).

The supply network 102 may include a source controller 106 and aprotection device 110, which may be an independent device or part ofanother device such as a supply controller. In some implementations thesource controller 106 includes a charge controller that regulates therate at which electric current is added to or drawn from the powersource 108 to regulate the network voltage. The source controller 106may include a maximum power point tracker (MPPT) that optimizes a matchbetween the sources of power within power source 108. In someimplementations, the power source 108 comprises an AC system oradditional DC networks of sufficient size (e.g., an AC power gridsystem). The source controller 106 may include a power inverter thatconverts excess DC power in the load network to supply AC power back tothe AC system of sufficient size. In such implementations, the systemmay operate with storage at the supply other than the AC system ofsufficient size. The source controller 106 and the power source 108 maybe a single integrated unit or two or more separate units. Theprotection device 110 may be a power converter such as a DC-to-DCconverter. The protection device 110 may be integrated with the sourcecontroller, it could be independent, or several protection devices couldbe distributed along the network.

The supply network 102 may employ the back-up power sources in powersource 108 to supply power at predictable levels. The supply network mayact as a voltage source to the load networks 120 and 160. The supplycontroller may ensure that the voltage in the network is controlledand/or it may ensure that any level of current required to maintainvoltage constant or ramping and in accordance with a preprogrammed loadcurve is supplied. In this instance, the load curve may be a voltagecurve. The amount of current required to maintain the voltage profilesis predictable so small variations of the current needed to provide thevoltage profiles indicate a network fault. Similarly, the protectiondevice 110 can monitor the rate of change for the current and/or thelevel of current to determine when a network fault occurs. The rate ofchange measured using a number of techniques. For example, it may bemeasured using an algorithm that calculates the derivative of thecurrent signal. Alternatively, it may be measured using one or morecircuits for measuring the rate of change for the current.

The power source 108 may allow independent load networks to control thecurrent flow with a level of I_(n) from the supply network 102 accordingto a preprogrammed load curve. For example, the power source 108 mayprovide additional DC power flowing through the at least a portion ofprotection device 110 during peak power consumption periods, low powerproduction periods, and/or unanticipated power demands. Additionally,the power source 108 may receive excess DC power provided by otherelements in the supply network 102 during high power production periodsand/or during low power consumption periods, and the power source 108may also receive power from the load networks 120 and 160.

In some embodiments, such as the one in FIG. 11, the supply network 1102can be generalized to have a protection device 1110 between the supplynetwork 1102 and the load networks. Supply network 1102 may operate in amanner similar to that described above for supply network 102.

In some embodiments, such as the one in FIG. 12, the supply network 1202includes a power supply 1204, a storage controller 1206, an energystorage 1208, and a supply controller 1210. The power supply 1204 andenergy storage 1208 may operate in a manner similar to that describedabove for the power source 108. Similarly, the storage controller 1206may operate in a manner similar to that described above for sourcecontroller 106. Additionally, supply controller 1210 may coordinate withenergy storage 1208 to supplement the power from power supply 1204 andmaintain the supply voltage at a desired level. Supply controller 1210can contain a protection device that operates in a manner similar tothat described herein for the protection devices 110 and 700. The supplycontroller 1210 may also perform other functions known in the art toregulate the power, voltage, and current that flows between the supplynetwork 1202 and the load networks 1220 and 1260.

Load Networks

The load network 120 may include a storage controller 126, an energystorage unit 128, and a load controller 130. In some implementations,storage controller 126 may be optional. In some implementations, theenergy storage unit 128 includes one or more batteries of appropriatesize(s), and the storage controller 126 includes a charge controllerthat controls the rate at which electric current is added to or drawnfrom the energy storage unit 128. The storage controller 126 may be usedby the load controller 1130 to limit the rate of change in the loadnetwork 120 slowly enough that the change can be differentiated fromother transience that occurs during normal operation of the system. Therate of change used may depend on the capabilities of the system. Thestorage controller 126 and the energy storage unit 128 may be a singleintegrated unit or two or more separate units. The load controller 130may be a power converter such as a DC-to-DC converter. The storagecontroller 126 may also communicate with the load controller 130 toadjust a position on the preprogrammed load curve based on the amount ofenergy stored in the energy storage unit 128. In this way, the storagecontroller 126 may operate to prevent the energy storage unit 128 frombeing fully charged or discharged, which would inhibit the ability ofthe load controller 130 from keeping the current drawn by the loadnetwork 120 in compliance with the preprogrammed load curve. The loadcontroller 130 may also be connected to one or more other devices suchas a photovoltaic power sources, a generator, etc.

The load network 120 may employ the energy storage unit 128 and loadcontroller 130 to maintain power flow at stable levels. The energystorage unit 128 may supplement the current flow to maintain a currentlevel of I₁ into the load network 120 according to a command from loadcontroller 130 based on a preprogrammed load curve. For example, theenergy storage unit 128 may provide additional DC power to the load 140during peak power consumption periods, low power supply periods, and/orunanticipated power demands. Load 140 may be a single load or multipleloads. The energy storage unit 128 may also receive excess DC powerprovided to the load network 120 that is not used by the load 140. Insome implementations, the load controller 130 requests power from thesupply network 102 to provide constant low power flows for charging ofthe energy storage unit 128 in addition to satisfying the demand of theload 140. For example, trickle charging or other suitable techniques maybe used. In general, the various capabilities of the supply network 102(e.g., power supply, controller, and energy storage device) and thevarious capabilities of the load network 120 (e.g., controller andenergy storage device) allow the current flowing across the system to beas constant and low as possible. In yet other implementations, as shownin FIG. 13, other sources of power 1234 and 1274, such as a photovoltaicgenerator or a conventional power generator, could be connected to theload network. FIG. 13 is similar to FIG. 12, but has the power sources1234 and 1274 added to the load networks.

Similarly, the load network 160 may include a storage controller 166, anenergy storage unit 168, and a load controller 170. In someimplementations, storage controller 166 may be optional. In someimplementations, the energy storage unit 168 includes one or morebatteries of appropriate size(s), and the storage controller 166includes a charge controller that limits the rate at which electriccurrent is added to or drawn from the energy storage unit 168. Thestorage controller 166 limits the rate of change in the load network 160slowly enough that the change can be differentiated from othertransience that occurs during normal operation of the system, such aswhen devices are added or turned on. The rate of change used will dependon the capabilities of the system. The storage controller 166 and theenergy storage unit 168 may be a single integrated unit or two or moreseparate units. The load controller 170 may be a power converter such asa DC-to-DC converter. The load network 160 may also be connected to oneor more other devices such as a photovoltaic power source, a generator,etc.

The load network 160 may employ the energy storage unit 168 to maintainpower flow at stable levels. The energy storage unit 168 can be abattery or other means of storing energy. The energy storage unit 168may supplement the current flow to maintain a current level of I₂ intothe load network 160 according to a command from load controller 170based on a preprogrammed load curve. For example, the energy storageunit 168 may provide additional DC power to the load 180 during peakpower consumption periods, low power supply periods, and/orunanticipated power demands. The energy storage unit 168 may alsoreceive excess DC power provided to the load network 160 that is notused by the load 180. In some implementations, the load controller 170may request power from the supply network 102 to provide constant lowpower flows for trickle charging of the energy storage unit 168 inaddition to satisfying the demand of the load 180. Additionally, in someimplementations, the energy storage unit 168 may also supply power tothe supply network 102. In general, the various capabilities of thesupply network 102 (e.g., power supply, controller, and energy storagedevice) and the various capabilities of the load network 160 (e.g.,controller and energy storage device) may allow the flows across thesystem to be as constant and low as possible.

In some embodiments, such as the one in FIG. 11, the load networks canbe generalized to have isolation devices 1132 and 1172, load controllers1130 and 1170, energy storage 1128 and 1168, and loads 1140 and 1180.Each of these may operate in a manner similar to that described abovefor isolation devices 132 and 172, load controllers 130 and 170, energystorage 128 and 168, and loads 140 and 180, respectively. Not shown inFIG. 11 are the equivalents of power inverters 122 and 162 and storagecontrollers 126 and 166. In some embodiments, the loads may be DCpowered requiring a DC/DC converter instead of the mentioned inverters122 and 162. As described herein, some embodiments may include thosefeatures while others do not. Similar to the description for thesefeatures in FIG. 1, some embodiments based on the load networks in FIG.11 may include power inverters or storage controllers that operate in amanner similar to the ones described above.

In some embodiments, such as the one in FIG. 12, the load networks 1220and 1260 include isolation devices 1232 and 1272, load controllers 1230and 1270, power inverters 1222 and 1262, storage controllers 1226 and1266, energy storage 1228 and 1268, and loads 1240 and 1280. Each ofthese may operate in a manner similar to that described above forisolation devices 132 and 172, load controllers 130 and 170, powerinverters 122 and 162, storage controllers 126 and 166, energy storage128 and 168, and loads 140 and 180, respectively.

Connecting the Supply Network and Load Network

In a system with many load networks, each load network may be assigned apriority to access the supply network so that not all loads are rampingdemand at the same time. This network management may be accomplishedusing, for example, a token ring communication coupling the supply andload networks and/or an embedded sensing and activation method at eachload network that senses voltage changes on the system and monitors theactivity on the system to determine the load network's turn to activate.During times when a load network is waiting to access the supplynetwork, the load network may access local energy storage. In a systemwith many supply networks, the supply networks may be similarlyconfigured so that not all supplies are providing power at the sametime.

In the embodiment illustrated in FIG. 1, the load network 120 services aload 140. The load 140 may include loads of a building or otherstructure, which typically includes, for example, lighting, ventilationfans, appliances, and other electronic devices. The load 140 may also bea building itself. In some implementations, the load 140 may include anelectric vehicle charger. Additionally, the load 140 may include DCloads such as batteries deployed at load points (e.g., at the electricvehicle charger), or an oven or heat pump. If the load 140 includes anAC load, the load network 120 may include a power inverter 122 thatconverts the DC power provided by the supply network 102 to AC power forthe AC load. The controlled flow and protection techniques describedherein may also be applicable to higher energy applications where theend load is variable. In particular, similar controlled DC distributionmay be used inside homes or businesses where batteries are installed toserve a single appliance to remove random load variations, causing thesystem to resemble a smaller version of the network 100 described. Thisallows higher energy application within the homes or businesses to usesimilar DC power control and protection techniques described in thisspecification. Similarly, the pulse communications described in thisspecification can also be included in these smaller implementations suchas when the network principles are applied to a single appliance.

Similar to load network 120, the load network 160 services a load 180.The load 180 may include loads of a building or other structure, whichtypically includes, for example, lighting, ventilation fans, appliances,and other electronic devices. The load 140 may also be a buildingitself. In some implementations, the load 180 may include an electricvehicle charger. Additionally, the load 180 may include DC loads such asbatteries deployed at load points (e.g., at the electric vehiclecharger), or an oven or heat pump. If the load 180 includes an AC load,the load network 160 may include a power inverter 162 that converts theDC power provided by the supply network 102 to AC power for the AC load.The controlled flow and protection techniques described herein may alsobe applicable to higher energy applications where the end load isvariable. As previously described, similar controlled DC distributionmay be used inside homes or businesses where batteries are installed atthe appliance level to remove random load variations. This allows higherenergy application within the homes or businesses to use similar DCpower control and protection techniques described in this specification.

As previously explained, the supply controller 106 may be programmed tomaintain the system voltage by supplying current to the load networks120 and 160 in accordance with the maximum load levels and ramp ratesspecified by the preprogrammed load curve 200. The load controllers 130and 170 may be constant current devices that request current from thesupply network 102 in accordance with the respective load levels andramp rates specified by the preprogrammed load curves 300 and 400. Theprotection device 110 may be programmed with a supply behavior that isshaped and matched to the accumulated load behaviors programmed in theload controllers 130 and 170 resulting in a limit load curve similar to200. As shown in FIGS. 2-4, the portion of the preprogrammed maximumload curve 200 between specific current levels, e.g., 3 and 9 amps, maybe compared and matched to the measured load curve that includes thecurrent I₁ used by load controller 130 of the load network 120 and thatfollows the preprogrammed load curve 300. The values of 3 and 9 amps areexemplary, other value may be more appropriate depending on theparticular application and conditions. The portion of the maximumpreprogrammed load curve 200 between specific load levels 0 and 3 may becompared and matched to the measured load curve that includes thecurrent I₂ used by load controller 170 of load network 160 and thatfollows the preprogrammed load curve 400. The preprogrammed expectedcurve 200 may take in account conditions where both I₁ and I₂ arechanging simultaneously. This strategy may enhance the performance ofthe system and may provide a protection system that reacts faster tofault conditions.

Load Curves

The control of the loads is designed to use the energy storage in theload networks to manage the load or supply variations to the loadnetwork. This allows the load controller to maintain a known currentthrough current levels and ramp rates, known as load curves which arepreprogrammed into the network. These preprogrammed load curves allowprotective elements or devices to sense, through current and/or voltage,that the system is within the acceptable operation conditions. Forexample, the worst case scenarios of ramp rate and/or current levels maybe determined based on the preprogrammed load curves from each of theload networks. By imposing limits or ramp shapes on the system, thesystem can ensure a relatively small rate of change.

Supply Network (First) Preprogrammed Load Curve

FIGS. 2 and 14 show examples of a preprogrammed worst case expected loadcurve 200 that may be used by the protection device 110 to compare withthe measured power flow from the supply network 102. The preprogrammedload curve 200 represents anticipated total usage by the load networks120 and 160 that should not be exceeded under non-faulted operation. Thepreprogrammed load curve 200 specifies protocols following specific ramprates and strategic current ranges (also referred to as specific loadlevels) for providing current to the load networks 120 and 160. Theexpected preprogrammed load curves are independent of the randomcurrents provided by the regulated power source 108. Currents suppliedby the supply network may be managed in part by the power source 108 bycompensating for fluctuations in the demand by the load networks. Whencurrents to, and from, the load networks are managed and predictable,the system voltage can be precisely maintained and the fluctuations canbe pre-estimated.

Controlling the voltage and current variations on the networks may allowthe network to quickly determine when the voltage or current changesquicker or slower than designed. Sensing these abnormalities may enablethe network to detect a number of problems including bad connections orarcing faults, which traditional fault detection systems cannot detect.For example, the protection device 110 may be programmed to respond tochanges in supply levels by comparing the current supplied with one ormore specified expected load curves 200.

Load Network (Second) Preprogrammed Load Curve

FIGS. 3 and 15 show examples of a preprogrammed load curve 300 that maybe used by the load controller 130 to draw current from the supplynetwork 102. The preprogrammed load curve 300 is based on usage by theload 140 and changes by specific amp increments with specific ramprates. The preprogrammed load curve 300 specifies protocols followingspecific ramp rates and in some cases strategic current setpoints (alsoreferred to as specific load levels) for receiving current from thesupply network 102, which may be independent of the random currentsprovided by the power source 108 and required by the load 140. The loadcontroller 130 may be a constant current device such that when the loadrequires changes in power, the power is provided or absorbed by theenergy storage unit 128 so that the supply network can ramp to the newappropriate setpoint. The energy storage unit 128 in combination withthe storage controller may reduce variation in the currents demanded bythe load network by compensating for fluctuations in the power demandedby the load 140. Additionally, the energy storage unit 128 may providethe power demanded by the load 140 between the times t1 and t2, duringwhich the load controller 130 is not requesting current from the supplynetwork 102. When current from the supply network 102 to the loadnetwork 120 is managed and predictable, the system voltage may beprecisely maintained with enhanced stability.

The load controller 130 may act as a constant current load at itsvarious setpoints. For example, the load controller 130 may beconfigured to request 6 amps from the supply network 102 over a widerange of DC network voltages. As other loads ramp up, the voltage dropson the system, which typically increases all load currents. To maintainconstant power to the load, the current may remain constant as theadditional power to the load 140 is extracted from the energy storageunit 128. In this system design, the load is seen as a constant currentor a known ramping current to a new setpoint. The actual current drawnfrom the supply network 102 by the load controller 130 may be determinedby a process that senses a set of parameters such as the draw of theload 140, the state of charge of the energy storage unit 128, and thetime of day. In some cases, the load controller 130 may request from thesupply network 102 a high current supply as it exercises a strategy tomeet the load demand and reinstate the battery charge to a high level inanticipation of a future time where the system may not be available todeliver current at a high level.

FIGS. 4 and 16 show examples of a preprogrammed load curve 400 that maybe used by the load controller 170 to manage power flow into the loadnetwork 160. The preprogrammed load curve 400 is based on the usage bythe load 180 and changes by specific amp increments with specific ramprates. Further, the preprogrammed load curve 400 may be the same ordifferent from preprogrammed load curve 300 based on the needs of loads140 and 180. The preprogrammed load curve 400 specifies protocolsfollowing specific ramp rates and in some cases strategic currentsetpoints (also referred to as specific load levels) for receivingcurrent from the supply network 102 which are independent of the randomcurrents provided by the power source 108 and required by the load 180.The load controller 170 may be a constant current device such that whenthe load requires changes in power, the power is provided or absorbed bythe energy storage unit 168 so that the supply network can ramp to thenew appropriate setpoint. The energy storage unit 168 and the storagecontroller 166 may manage variation of the currents received by the loadnetwork 160 by compensating for fluctuations in the power demanded bythe load 180. Additionally, the energy storage unit 168 may provide thepower demanded by the load 180 between the times t3 and t4, during whichthe load controller 170 is not requesting current from the supplynetwork 102. When current from the protection device 110 to the loadnetwork 160 are managed and predictable, the system voltage may beprecisely maintained.

The load controller 170 may act as a constant current load at itsvarious setpoints. For example, the load controller 170 can beconfigured to request 3 amps from the supply network 102 over a widerange of DC network voltages. As other loads ramp up, the voltage dropson the system, which typically increases all load currents. In thissystem design, the load may be seen as a constant current or a knownramping current to a new setpoint. The actual current drawn from thesupply network 102 by the load controller 170 may be determined by analgorithm that senses a variety of parameters such as the draw of theload 180, the state of charge of the energy storage unit 168, and thetime of day. In some cases, the load controller 170 may request from thesupply network 102 a high current supply as it exercises a strategy tomeet the load demand and reinstate the battery charge to a high level inanticipation of a future time where the system may not be available todeliver current at a high level.

Pulse Signal Communication Platform

To communicate between the supply network and the load networks, thesupply network may use controlled voltage pulses where the ramp rate,level, or combination of the two (i.e. the shape of the change) of thatvoltage, is used to trigger specific events in the load network, such asswitching hardware on or off, adjusting power consumption, or limitingpower production. The pulses can also communicate other information suchas weather data, system setpoints, and other messages. By utilizing thealready present power lines, the pulse signal communication platform mayreduce the need for extra equipment and increases the reliability of thecommunication platform. So long as power is being transmitted, thesystem may be able communicate. In one possible plug-and-play controlscheme, the commands are not addressed to a specific element on thesystem but broadcasted to all the elements that respond based on thebroadcasted message. One example of such a control scheme is shown inFIG. 5. Alternatively, device specific commands may be sent using aseries of pulses. For example, a first pulse or set of pulses mayaddress the device followed by an additional pulse or pulses tocommunicate the command or information directed to the identifieddevice. An initial pulse identifying a communication as device specificor as a broadcast communication may also be used.

To send a pulse, the supply network may use regulating elements, such assupply controller 106, to slowly increase the voltage in the power linefrom an initial level to a predetermined voltage, or communicatingvoltage, that the load network knows indicates the change in voltage isa message. While the examples herein use an increase in voltage as anexample, decreases in voltage may also be used. The load network thenuses the non-regulating elements to receive and decode the communicatingvoltage. The non-regulating elements may include the protection device110, the load controllers 130 and 170, or discrete devices such asvoltage sensors that allow the non-regulating elements to receive andmeasure the voltage changes. For example, the voltage sensor,processor(s) and memory device(s) necessary to receive and decode thepulse may be included in the load controllers 130 and 170. Afterreceiving and measuring these changes, the non-regulating elements use aset of pre-programmed instructions to decode the signal.

In one embodiment, the communications may be sent using slow pulses withdurations of hundreds of milliseconds or a few seconds. By using slowpulses instead of high frequency signals the interference coming frompower conversion equipment and resonances and delays created by longtransmission line effects are eliminated. Furthermore, the use of lowfrequency pulses enables transmitting the information for long distancesnot achieved with high frequency pulses. These slow pulses may be anyvalue slower than the normal operation of the system, such as turning onor connecting devices. For example, a slower pulse may be 10 timesslower or 100 times slower than the normal operation depending on thecapabilities of the system to reliably control the normal operation ofthe supply to the loads.

In one embodiment, decoding the signals consists of measuring how longthe voltage is set to the communicating voltage. In this embodiment,different lengths of time the system stays at the communicating voltagewould indicate different commands or messages. For example, one lengthof time may mean to switch the device on or off, a second length of timemay instruct the load network to limit power consumption. Similarly,commands or messages may also be communicated through the shape of thepulse in the voltage or current, or through the ramp rate of the voltageor current.

Other conditions, such as a fault, may also cause the voltage to reachthe communicating voltage. To prevent the non-regulating elements frominterpreting these changes as a message, the supply network maygradually increase the voltage at a set rate to indicate that the changein voltage is a communication. This process is also referred to as aslow ramp up of the voltage. Similarly, the supply network may graduallydecrease the voltage to the normal level to indicate the message isover. This process is also referred to as a slow ramp down. FIG. 6 showsone example of a communication pulse with a slow ramp up and down. FIG.17 shows another example of a communication pulse with a slow ramp upand down. The ramp up and ramp down rates themselves, while slow, couldbe changed and used to communicate information in addition to the pulseduration.

The pulse communication platform may also include error correction. Forexample, errors in detection can be actively corrected by the elementre-sending the command, such as a supply controller, if the expectedresponse does not occur within a certain time period from thecommunication

While the above has described a pulse communication platform thatcommunicates from the supply network to the load network, otherconfigurations are also possible. For example, the load network cancommunicate with the supply network, by imposing current pulses on I₁ toI_(n), the pulse communication network can be used to communicatebetween any network or device that is connected through a power line solong as the system is transmitting power.

Fault Detection Detecting a Fault

For fault protection, the supply network 102 includes a protectiondevice 110. In other embodiments, the protection device 110 may belocated within the load network, such as within the load controllers 130and 170. The protection device may be internal or external to a supplycontroller. Multiple protection devices may be placed along thedistribution line allowing sectioning the line and coordinated detectionof faults. The protection device 110 may include solid state relays orother types of suitable electrical isolators. The protection device 110operates to isolate the load networks 120 and 160, remove the energystored in the distribution lines, shut down other converters, or shutdown other energy sources when a fault condition is detected.

In particular, the balancing strategy allows the system 100 to reactquickly to an imperfect match between the supply and expected loadbehavior by a voltage variation or current variation beyond a finespecified threshold. The voltage variation indicates a voltage imbalanceand thus a current imbalance. Traditional systems must tolerate a widerange of operating currents such that even in fault conditions it takestime for the system to determine that the current is abnormal andconstitutes a fault. Some embodiments of the system described in thisspecification assume anything other than the expected very narrow rangeof current levels, changes, and shapes constitutes a fault and tripsmore quickly. The protection may be triggered based on inconsistencieswith a threshold of variances in the current levels, shape, and/or ramprate as determined by the preprogrammed load curves. This threshold ofvariance may be determined based on each independent load curve or canbe based on when the threshold of variance is exceeded by more than one,or all, of the load network preprogrammed load curves in the system.This is made possible because the system removes random currentvariations to regulate the current levels, allowing fine tolerances tobe set for absolute current level protection. Additionally, because thesystem controls rates of change or current and voltage, as well as theshape of change (or ramp rate and shape) these values, rate of changeand shape of change may be used to determine faults. For example,whereas a classical protection system triggers a fault when it detectsvariance at 150% above the load after a time delay, the current systemmay be able to trigger a fault protection scheme for smaller variances,such as 5% above load. Additionally, the current system may be able toinstantaneously trigger a fault.

Clearing the Fault and Re-Energization

In the event of any variance outside a specified band, which indicatesthat the power supply or a power demand does not conform with thecorresponding preprogrammed load curve, the protection device 110 may beactivated to de-energize the system. Alternatively, the protectiondevice 110 may de-energize the system by sending a signal to otherdevices to trip. The protection device 110 may be implemented usingsemiconductor switches or relays that enable or disable current flow.Upon loss of supply network voltage for some short period of time, theload network isolation 132 and 172 opens. The protection device 110 maythen re-energize the system 100 with no loads connected.

Upon sensing voltage, the isolation devices 132 and 172 in the loadnetworks 120 and 160 may close in sequence by a control signal orthrough an embedded algorithm. If a protection device closes and thesystem 100 detects an imbalance, the protection device 110 may betripped, and the protection device close sequence may start again, butthis time with the faulty segment remaining isolated through embeddedlogic.

In one embodiment, the load controllers 130 and 170 in the load networksmay be programmed to delay the start of power exchange between the loadnetwork and the supply network. The delay gives enough time for a simpleand low current re-energization of the line under no load, as describedabove, and also enables the system to easily identify whether the faulthas cleared. The protection device 110 may detect that the fault hascleared when the load network does not consume power during there-energization delay. However, the protection device 110 may detectthat the fault has not cleared when the load network does consume faultcurrent during the re-energization delay.

During re-energization, the system 100 can be cleared without impact tothe supply network 102 due to the power source 108 which maintains powerin the event that a load network is disconnected, and without impact tothe load networks 120 and 160 due to the respective energy storage units128 and 168 which provide power to the respective loads 140 and 180 inthe event that one or both load networks 120 and 160 are disconnectedfrom the supply network 102. In other words, the power source maycontinue to operate, supplying its power to other elements and loadnetworks 120 and 160 may continue to operate by supplying power storedin the respective energy storage units 128 and 168 to the respectiveloads 140 and 180.

The Protection Device

FIG. 7 shows a block diagram of the protection device 700 connected tothe main line 712 and load networks, or prosumers, 714. The loadnetworks 120 and 160 integrate energy storage and in many casesrenewable generation so that the change in current demanded or providedthrough the protection device is limited and known.

The protection device incorporates a sensing unit 702 that can detectcurrent and/or voltage to measure, with high bandwidth, the currentgoing to the load networks 120 and 160. Devices need high bandwidth toallow them to detect transients in current or voltage at frequencieshigher than the frequencies during normal operation. The currentmeasurement may be sent to a controller 704, which may include aprocessor and memory, that calculates the derivative of the current,which represent the rate of change of the current. The controller 704may be programmed with maximum current ramp rates monitored by the di/dtlimiter 718 that are indicative of normal operation. Controller 704 maycompare the calculated rate of current change, or derivative of thecurrent change, based on the measurements with the maximum current ramprates. If the measured rate of change is outside the normal range, thecontroller 704 may open a fast disconnect 706, such as those based onsemiconductor devices or solid-state relays, and interrupt the currentflow. Controller 704 may also activate a low current, slow respondingenergization device, such as energization device (e.g., a relay orsemiconductor) 708, to energize the previously faulted line. In otherembodiments, the energization relay 708 may alternatively be asemiconductor or other devices known in the art. The current flowingthrough energization relay 708 may be limited by a current limitingdevice 710, for example, a resistor. Depending on the current flowingthrough the current sensor 702 when the energization device 708 isactivated, the controller 704 can decide if the fault has been cleared.

The controller 704 may incorporate a communication platform with anexternal controller that enables changing the settings for normal andabnormal rate of current change. The re-energization of the line couldbe automatically programmed, manually initiated, or remotely initiatedthrough the communication link. A fault current ramp limiting device 710that may be an inductor that can be inserted in series with the fastdisconnect 706 to limit the rate of change of the fault current orvoltage. The addition of inductors into the system runs counter tocurrent logic, which seeks to eliminate inductance because it limits therate of change. In the disclosed system, however, the system is designedto keep the rate of change low. Accordingly, inductors may be introducedto slow the rapid current spikes that typically occur during DC linefaults. This allows fuses, and other protection mechanisms with lowercurrent ratings to be employed, which are typically cheaper and saferthan higher current alternatives. Classic overcurrent protections canalso be included in the device for extra protection or to respond if theprotection fails.

Smart Inverters

In another embodiment, the network includes a smart inverter thatprotects equipment supplied from the inverter AC output by improvingspeed of operation and increasing the number and types of faults thatcan be detected and cleared including faults that would not damage theinverter but that could result in damage to external equipment or unsafeconditions for the users. The smart inverter system described detectsand/or measures the AC output of the inverter to analyze whether a faulthas occurred and can then control the inverter and other devices in thepower grid network to protect the power grid network and any devicesconnected to it from damage due to faults.

In one embodiment, the smart inverter includes a processor and storagedevice that can perform the analysis necessary to analyze the currentand shut down the inverter when a fault occurs. In another embodiment,the inverter can be connected to a control unit with a processor andstorage device. The control unit performs the analysis necessary toanalyze the current and shut down the inverter. Both embodiments mayalso communicate with other devices in the power grid network, such as acircuit breaker or fuse box to trigger other power grid protectionprotocols when a fault occurs.

The Inverter

Several forms of inverters are known in the industry. The presentinvention can utilize a control unit added to an inverter to bothmonitor the output of the inverter and control the inverter when a faultis detected.

FIG. 8 is a diagram illustrating an example of an inverter 802 that canbe used in this system. Other configurations for the inverter are alsoknown and can achieve the invention. Inverter 802 includes an input 804to receive a DC supply. The DC supply flows to a switch 806 thatalternates between at least two paths for the DC energy to flow. Thesetwo paths flow to magnetic components 808 to induce an AC supply flow.That AC supply flow is an output of the filter 810 with typical ACsupply properties such as current and voltage that can be measuredeither within the inverter 802 or as the flow leaves the inverter 802.

The switch 806 can take several forms as known in the art. For example,an electromechanical version allows the switch 806 to connect to twocontact points where the switch 806 is biased towards one contact pointby a spring. An electromagnet is connected to the first contact andpulls the switch towards the second contact. When the switch 806 reachesthe second contact, the current to the electromagnet is interrupted andthe electromagnet turns off, allowing the spring to move the switch 806back to the first contact. This allows the switch 806 to alternaterapidly between the two contact points, sending flow through the twopaths to create the AC supply. Other configurations for the switch 806known in the art can also be used. For example, semiconductor switches,transistor switches, thyristor switches, and more.

The above description produces a square wave, but some load networkswill need a smooth, sinusoidal wave form. In another embodiment, theinverter 802 may also include hardware that allows the inverter tocreate the AC supply as a smooth, sinusoidal wave or other wave formsknown in the art. To create this smooth, sinusoidal wave form, theinverter can include capacitors, inductors, low-pass filters, resonantfilters, rectifiers, antiparallel diodes, and other devices known in theart. This same hardware can also be used to create other wave forms suchas modified sine waves known in the art.

The Control Unit

In one embodiment, the control unit 812 includes processor(s) 814 andmemory storage device(s) 816. The memory storage device (s) 816 storesthe instructions to be carried out by the processor(s) 814 and the datanecessary to execute those instructions, such as parameters for thenormal operation of the power grid and the conditions that mean a faulthas occurred.

The processor(s) 814 may be implemented as one or more known or customprocessing devices designed to perform functions of the disclosedmethods, such as single- or multiple-core processors capable ofexecuting parallel processes simultaneously. For example, theprocessor(s) 814 may be configured with virtual processing technologies.The processor(s) 814 may implement virtual machine technologies,including a Java virtual machine, or other known technologies to providethe ability to execute, control, run, manipulate, store, etc., multiplesoftware processes, applications, programs, etc. One of ordinary skillin the art would understand that other types of processor arrangementscould be implemented that provide for the capabilities disclosed herein.

The memory storage device(s) 816 may include instructions to enable theprocessor(s) 814 to execute programs, such as one or more operatingsystems, server applications, communication processes, and any othertype of application or software known to be available on computersystems. The memory storage device(s) 816 may be implemented in volatileor non-volatile, magnetic, semiconductor, tape, optical, removable,non-removable, or another type of storage device or tangible (i.e.,non-transitory) computer-readable medium.

In some embodiments, the memory storage device(s) 816 includesinstructions that, when executed by the processor(s) 814, perform one ormore processes consistent with the functionalities disclosed herein.Methods, systems, and articles of manufacture consistent with thedisclosed embodiments are not limited to separate programs or computersconfigured to perform dedicated tasks.

FIG. 9 is a flowchart illustrating the steps of an exemplary faultdetection process 900 performed by the processor(s) 814 in accordancewith the disclosed embodiments. However, the steps illustrated by theflowchart are only exemplary, and one or more steps may be added ordeleted to implement fault detection process 900. Additionally, thesteps may be performed in any order that allows the system to detect afault.

At step 910, the control unit 812 receives an output from the inverter802. This output can be the current, or the voltage. Alternatively, theoutput from the inverter can be measurements of the current or voltagefrom the inverter.

At step 920, the storage device(s) 816 store the outputs from theinverter 802 for multiple points in time. This allows the processor(s)814 to access data sufficient to determine and analyze how the outputhas changed over time. For example, the processor(s) 814 could determinethe absolute values of the current across a minute, or the rate at whichthe current changes across a minute or the difference between currentsmeasured at different points.

At step 930, the processor(s) 814 analyze the output from the inverter802 to determine whether a fault has occurred. There are numerous typesof faults that can be detected with this system including GFI,overcurrent, unbalanced voltage (open neutral), and arcing faults.

As one example, a GFI fault can be detected by analyzing the flow ofelectricity leaving the inverter 802 using either the voltage orcurrent. A GFI fault can be detected by analyzing the flow ofelectricity at a point where the inverter connects to the load 140 or160. In this example, ground faults result in current flowing from theinverter 802 output to the ground via the fault and returning throughthe grounding terminal of the inverter 802. In normal, not faultedconditions, the current flowing through the ground is zero and thealgebraic sum of the current flowing through the terminals should bezero. However, when a ground fault occurs, the sum deviates from zero.If the inverter 802 is provided with current sensors in all the powerlines as shown in FIG. 8, the measured currents could be added(I_(total)=I_(A)+I_(n)+I_(B)) and if the result drifts from zero, thesystem could conclude that there is a ground fault somewhere in theoutput line. Alternatively, the inverter 802 can receive the currentmeasurements by a residual current sensor, which physically measures thesum of the three currents and the output of the sensor could be used todetermine if there is a ground fault.

As another example, an external arc fault can be detected using theinverter hardware. Traditionally, AC arc fault detectors are providedexternal to the inverters and using separate sensors from the ones usedfor inverter power control. The inverter 802 can measure the powersignal through the outputs as described herein. The control unit 812 maythen apply signal processing with internal algorithms known in the artto identify external arc faults based on those measurements, such ascurrent measurements.

As another example, the inverter 802 could detect an open neutral faultbetween the inverter 802 and the load. In some embodiments, the inverter802 may produce a split phase power signal, which provides twosinusoidal voltages out of phase by 180 degrees. These may include acommon point, or neutral, that allows some loads to be placed from lineto line so that they receive twice the phase voltage or receive thephase voltage, while others are connected. These types of systems arecommon in residential applications. In this embodiment, the inverter 802independently regulates the voltage of each of the two phases andmaintains the 180 degrees phase shift to produce the split phase. Usingsplit phase configurations can sometimes result in damage to the neutralconductor, creating an open neutral fault that could produce overvoltages in some of the loads connected between phase and neutral.

In some embodiments, the inverter could be used to detect an openneutral fault. One characteristic of split phase systems is that thecurrent flowing through the two lines is typically identical, orbalanced. In this case, the inverter 802 current measurements may readzero current in the neutral. However, a reading of zero in the neutralcould also be due to an open neutral fault. If the inverter is providedwith a neutral current sensor, and the current becomes zero (In=0), theprocessor(s) 814 in the control unit 812 may command the inverter 802 toproduce a small deviation in magnitude or phase of the voltage betweenthe two phases (e.g., VAn>VBn). In this instance, the voltage in onephase is now slightly different from the voltage on the other phase orthe phase angle is not exactly 180 degrees, making the previouslybalanced loads out of balance and producing current through the neutral.The control unit 812 may then verify that the neutral connection isstill intact. If the deviation in voltage does not produce a measurableneutral current, the control unit may conclude that there is an openneutral fault.

In other embodiments, the neutral current does not have to be measured.The neutral current may alternatively be calculated as the algebraic sumof the two-phase currents (I_(n)=I_(A)+I_(B)). In this embodiment, theinverter 802 described herein may then use this calculated value inplace of the measured value to detect the open neutral fault.

At step 940, the processor(s) 814 determine whether to enter one of theprotection modes stored on the storage device(s) 816. The storagedevice(s) 816 can store one or more protection modes for protecting thenetwork. One of these protection modes can be a shut off of theinverter's 802 switching operation, stopping the flow of AC current.Other protection modes could include tripping a circuit breaker to stopthe flow of AC current or causing a fuse box to blow a fuse.

At step 950, the processor(s) 814 issue a command to the appropriatedevice to enter the protection modes selected to protect the power gridsystem 100. For example, these commands can be sent to the inverter 802,a circuit breaker, or a fuse box.

In one embodiment, the control unit includes a sensor that measures theAC supply of the inverter 802. This sensor can measure the current,voltage, and/or any other relevant characteristic of the AC supply.

Inverter and Control Unit Incorporated Together

FIG. 10 is a block diagram illustrating another embodiment where thecontrol unit, including processor(s) 1002, memory storage device(s)1004, and communication platform 1006, is incorporated into the inverter1000. In this embodiment, both the inverter 1000 and the control unitoperate in the same way as inverter 802 and control unit 812 describedabove.

Advantages/Uses

This technique is different from traditional approaches that rely on alarge energy flow to the fault to initiate protective action. Rather,this technique uses the predictability of the current flows to emulate amulti-terminal differential current protection scheme. Any current flowthat deviates from the preprogrammed load curves indicates a systemvoltage or current that does not correspond to the expected predictedvoltage or current profiles. Because current limited active powersources will not provide current to trip breakers or blow fuses, highresistance faults and in line arcing may go undetected in conventionalpower grid systems. Fault conditions are not consistent with theexpected current and voltage profiles in embodiments of the invention,and therefore the system 100 would trip and isolate the problem. Thisfault detection approach provides a faster response to fault conditionswith better reliability, less damage, and higher safety relative toconventional power systems and other DC power techniques withoutrequiring communication with other components of the power grid system100 and without requiring current sensing by additional currentmeasurement devices at remote terminals.

To improve the economics and safety of the system 100 as a whole, theload battery and its power inverter can be configured to replace thetraditional metering and main panel protection at the load network.Embodiments of the invention leverage the high switching speed of apower inverter by using current sensing circuits and solid-state relaysto replace the traditional panel circuit breakers. When a faultsituation is detected, the power inverter is disabled instantly, and theappropriate circuit is isolated by opening the relay, so the powerinverter can return to service safely. The safety of full system groundfault protection can be increased using such a design.

Additional embodiments exist that apply the principles of this inventionto systems ranging from appliance-level power control to single buildingpower control, to entire power grid control. Any system configured touse storage or additional power sources to eliminate the need for randomflows across the network can implement the principles disclosed. Forexample, when the system is implemented in a home and the load iscompletely DC, the energy storage may be distributed within the home andsupplied by the DC controller using voltages low enough to eliminate theneed for grounded fixtures, lowering the cost of installationsignificantly. Building on the concept of power over Ethernet and thetechnique described above of constant power supply to load networks withstorage, the system may incorporate small scale energy storage at everyappliance which consumes more than 100 watts peak (or another standardlevel). An appliance may be more efficient if it operates constantly atlower loads (e.g., a refrigerator with a motor and compressor that arefar too big if it cycles and runs only half the time), or if a dedicatedenergy storage is charged with a low constant supply and drawn from whenthe appliance is in operation.

A few implementations have been described in detail above, and variousmodifications are possible. For example, in implementations where thecharacteristics of a power source is predictable and consistent, asupply network may not include a storage controller and an energystorage unit as a power buffer. Similarly, in implementations where thecharacteristics of a load is predictable and consistent, a load networkmay not include a storage controller and an energy storage unit as apower buffer. While the implementations described focus on DC systems,these implementations may also apply to AC systems.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of what may be claimed, but ratheras descriptions of features that may be specific to particularembodiments. Certain features that are described in this specificationin the context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

1.-38. (canceled)
 39. A load system, comprising: a load controller; atleast one processor; and a computer-readable medium containinginstructions that, when executed by the at least one processor, causethe load system to perform operations comprising: determining a loadcontrol curve, the load control curve: specifying a current draw orsupply of the load controller as a function of time; including at leasttwo current setpoints; and including transitions between the at leasttwo current setpoints, the transitions having specified ramp rates, thespecified ramp rates having amplitudes less than or equal to one or morepredetermined maximum ramp rate amplitudes; and configuring the loadcontroller to draw from or supply current to a distribution circuitconnected to the load controller based on a present time and the loadcontrol curve.
 40. The system of claim 39, wherein the load controllercomprises a DC-to-AC power converter.
 41. The system of claim 39,wherein: the amplitudes comprise RMS amplitudes; and the load controlleris configured to draw from or supply alternating current to thedistribution circuit.
 42. The system of claim 39, wherein the loadcontroller is contained in lighting equipment; heating, ventilation, orair conditioning equipment; battery charging equipment; or an appliance.43. The system of claim 39, wherein: the system further comprises anenergy storage device; and the load control curve is determined at leastin part on based on charge information received from the energy storagedevice and a current draw of a load.
 44. The system of claim 43,wherein: the load control curve is independent of a present current drawof the load.
 45. The system of claim 43, wherein: the load control curveis configured to cause a predicted charge level of the energy storagedevice to have specified value at a specified future time.
 46. Thesystem of claim 43, wherein: the load control curve is configured tomaintain a predicted charge level of the energy storage device at alevel less than fully charged and more than fully discharged.
 47. Thesystem of claim 39, wherein: the operations further comprisecommunicating with a supply controller connected to the distributioncircuit.
 48. The system of claim 47, wherein: the communicationspecifies the load control curve.
 49. The system of claim 47, wherein:communicating with the supply controller comprises configuring the loadcontroller to impose one or more amplitude increasing or amplitudedecreasing current pulses on the current drawn from or supplied to thedistribution circuit.
 50. The system of claim 49, wherein: an amplitudechange rate of each current pulse is between 10 and 100 times less thanany of the one or more predetermined maximum ramp rate amplitudes. 51.The system of claim 39, wherein: the operations further comprisereceiving an assigned priority from a supply controller connected to thedistribution circuit and the load control curve is determined based atleast in part on the assigned priority.
 52. The system of claim 39,wherein: the load system comprises an isolation system; and theoperations further comprise: detecting de-energizing of the distributioncircuit; isolating the load system from the distribution circuit inresponse to the de-energizing; detecting re-energizing of thedistribution circuit; and ceasing isolation of the load system from thedistribution circuit in response to the re-energizing.
 53. A supplysystem, comprising: at least one processor; and a computer-readablemedium containing first instructions that, when executed by the at leastone processor, cause the supply system to perform operations comprising:determining a load control curve that specifies a current drawn from orsupplied into a distribution circuit as a function of time; anddetecting a fault associated with the distribution circuit by: comparinga present current drawn from or supplied to the distribution circuit tothe load control curve; or comparing the present current drawn from orsupplied to the distribution circuit to a predetermined maximum rampamplitude; and clearing the fault.
 54. The system of claim 53, wherein:detecting the fault comprises comparing the present current to the loadcontrol curve.
 55. The system of claim 54, wherein: comparing thepresent current to the load control curve comprises comparing a ramprate of the load control curve to a ramp rate of the present currentdrawn from or supplied to the distribution circuit.
 56. The system ofclaim 54, wherein: comparing the present current to the load controlcurve comprises determining that a difference between the presentcurrent and the load control curve exceeds a threshold.
 57. The systemof claim 54, wherein: comparing the present current to the load controlcurve comprises comparing a shape of the present current to a shape ofthe load control curve.
 58. The system of claim 53, wherein: the supplysystem further comprises a protection device; and clearing the faultcomprises disconnecting the distribution circuit from the supply systemusing the protection device.
 59. The system of claim 58, wherein: theprotection device is a semiconductor switch or relay.
 60. The system ofclaim 53, wherein: clearing the fault comprises providing secondinstructions to at least one load control system to isolate the at leastone load control system from the distribution circuit.
 61. The system ofclaim 60, wherein: providing the second instructions comprises imposingone or more voltage pulses of increasing amplitude or of decreasingamplitude on the distribution circuit.
 62. The system of claim 61,wherein: the one or more voltage pulses are distinguishable fromtransients associated with turning on, turning off, connecting, ordisconnecting devices to the supply system.
 63. The system of claim 53,wherein: the operations further comprise specifying when each of one ormore load control systems connected to the distribution circuit canrequest additional current from the supply system.
 64. The system ofclaim 53, wherein: the supply system further comprises: a storagecontroller; and an energy storage device; and the storage controller isconfigured to, at least in part, draw from or supply current into theenergy storage device.